[doc][embeddingapi] Add embedding User and Developer Guide

- Add Embedding_Testing_Suite_User_Guide.md
- Add Embedding_Test_Suite_Developer_Guide.md
- Add Embedding_Test_Suite_Packaging_Guide.md
Merge pull request #962 from zhuyongyong/yongzhu/embeddingapi-doc/md

[doc][embeddingapi] Add embedding User and Developer Guide